(1) Field of the Invention
The present invention relates to a semiconductor memory device. More particularly, it relates to a dynamic random access memory provided with a means for clearing the stored data of all bits at the same time.
(2) Description of the Related Art
In general, data stored in memory devices and used in, for example, a graphic display system or in a computer system which requires initialization must be quickly cleared at the same time.
Conventionally, in a dynamic random access memory, when the memory cells of all bits are to be cleared, data "0" is written by sequentially specifying addresses for respective memory cells.
However, such a conventional technique is disadvantageous in that a long time is necessary for clearing all the bits. In addition, a special circuit device or a program is necessary for providing the addresses of the memory cells to be sequentially cleared to the memory device.
Further, in a conventional dynamic random access memory, for the same input/output data, for example, "0", the memory cells on one side of the memory cell arrays with respect to sense amplifiers represent discharged states, and the memory cells on the other side of the memory cell arrays with respect to sense amplifiers represent charged states. That is, for the same input/output data, the one half of the memory cells do not store charges while the other half of the memory cells do store charges, and vice versa. In other words, the charging states of the memory cells for the same input/output data are different. Therefore, to clear all bits of the memory cells, that is, to input the same data "0" into all of the memory cells, one half of the memory cells should be discharged and the other half of the memory cells should be charged. The discharge of a number of memory cells at the same time on one side of the memory cell array is relatively easy. However, it is impractical to charge a number of memory cells at the same time on the other side of the memory cell array, because the charging of the memory cells requires a number of large power pull-up transistors, which disadvantageously occupy a large area and consume a large amount of electric power.